1. Field of the Invention
The present invention generally relates to an imaging device, and more particularly to a light sensitivity calibration method and system.
2. Description of Related Art
An image sensing element is one of important components of an imaging device, and is used to convert a light signal to an electric signal suitable to be post-processed by a processing unit. However, due to characteristic differences among the image sensing elements, the relationship between the light sensitivity in a preview mode and the light sensitivity in a capture mode generally cannot be maintained constant. Therefore, a need has arisen to calibrate the light sensitivity of preview mode and the light sensitivity of capture mode respectively.
An electronic shutter is ordinarily used to control exposure in the preview mode, and a mechanical shutter is ordinarily used to control exposure in the capture mode. The mechanical shutter has lower accuracy for the reason that a period of time, known as a lag time, is required from the beginning of shutting down the mechanical shutter until the mechanical shutter is completely shut down. As the mechanical shutters are distinct from each other, a need has thus arisen to calibrate the mechanical shutter of each imaging device in order to ensure exposure accuracy.
The calibration procedure for a mechanical shutter should be based on accurate light sensitivity. On the other hand, however, the calibration procedure for light sensitivity should be based on an accurate lag time of the mechanical shutter. In other words, the mechanical shutter calibration and the light sensitivity calibration rely on each other to provide an accurate value as the calibration basis in order to arrive at an accurate calibration result. The conventional calibration procedure for light sensitivity uses a predetermined lag time of the mechanical shutter. As discussed above, the predetermined lag time is usually not consistent with a real mechanical shutter of the imaging device. Accordingly, an accurate result for conventional light sensitivity calibration cannot normally be acquired.
For the foregoing reasons, a need has arisen to propose a novel light sensitivity calibration method used to alleviate the dilemma between the light sensitivity calibration and the mechanical shutter calibration.